When I was a kid growing up in the '70's in L.A., Pup 'n' Taco was a special place. Even more than Wienerschnitzel (or Der Wienerschnitzel as it was known), Pup 'N' Taco provided comfort food. I can remember my mom taking me there when I was sick and stayed home from school. Apparently, I was not to sick to enjoy a mustard dog.
Here's a classic commercial and some links around the web that will help you fellow Southern California kids remember: